First, an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) system is described below with reference to FIG. 1.
FIG. 1 illustrates a network structure of the E-UTRAN. The E-UTRAN system has evolved from the conventional UTRAN and basic standardization thereof is currently underway under the 3rd Generation Partnership Project (3GPP). The E-UTRAN system is also referred to as a “Long Term Evolution (LTE) system”.
The E-UTRAN includes eNode Bs (eNBs). The eNBs are connected through X2 interfaces. Each eNB is connected to User Equipments (UEs) and is connected to an Evolved Packet Core (EPC) through an S1 interface.
Radio interface protocol layers between UEs and the network can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the Open System Interconnection (OSI) reference model widely known in the field of communication. A physical layer included in the first layer provides an information transfer service using a physical channel. A Radio Resource Control (RRC) layer located at the third layer controls radio resources between UEs and the network. To accomplish this, the RRC layer exchanges RRC messages between UEs and the network.
FIG. 2 illustrates a radio interface protocol structure between a UE and a UTRAN based on the 3GPP radio access network standard. The radio interface protocol of FIG. 2 is divided horizontally into a physical layer, a data link layer, and a network layer and is divided vertically into a user plane for data/information transmission and a control plane for signaling. The protocol layers of FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the Open System Interconnection (OSI) reference model widely known in the field of communication.
A physical layer, which is the first layer, provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to a Medium Access Control (MAC) layer above the physical layer through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. Data transfer between different physical layers, specifically between the respective physical layers of transmitting and receiving ends, is performed through the physical channel. The physical channel is modulated according to Orthogonal Frequency Division Multiplexing (OFDM) method, using time and frequency as radio resources.
The MAC layer of the second layer provides a service to a Radio Link Control (RLC) layer above the MAC layer through a logical channel. The MAC layer may construct a MAC Protocol Data Unit (PDU) by attaching a MAC header to Service Data Units (SDUs) of an upper layer. The MAC PDU may include MAC Control Elements (CEs) which are control messages that can control functions of the MAC layer.
The RLC layer of the second layer supports reliable data transfer. A PDCP layer of the second layer performs a header compression function to reduce the size of each IP packet header containing relatively large, unnecessary control information in order to efficiently transmit IP packets such as IPv4 or IPv6 packets in a radio interval with a small bandwidth.
FIG. 3 illustrates an exemplary configuration of a MAC PDU in the related art. As shown in FIG. 3, the MAC PDU is divided into a MAC header and a MAC payload. The MAC payload may include zero or one or more MAC CEs and zero or one or more MAC SDUs. The MAC header includes one or more MAC sub-headers for the MAC CEs and the MAC SDUs included in the payload.
The Radio Resource Control (RRC) layer located at the top of the third layer is defined only in the control plane and is responsible for control of logical, transport, and physical channels in association with configuration, re-configuration, and release of radio bearers (RBs). The RB is a service that the second layer provides for data communication between the UE and the UTRAN. The UE is in a connected mode if there is an RRC connection between the RRC layer of the radio network and the RRC layer of the UE. Otherwise, the UE is in an RRC idle mode.
A Non-Access Stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management.
One cell included in the eNB is set to provide a bandwidth such as 1.25, 2.5, 5, 10, or 20 MHz to provide a downlink or uplink transmission service to a plurality of UEs. Here, different cells may be set to provide different bandwidths.
Downlink channels used to transmit data from the network to the UE include a Broadcast Channel (BCH) used to transmit system information, a Paging Channel (PCH) used to transmit paging messages, and a downlink Shared Channel (SCH) used to transmit user traffic or control messages. Control messages or traffic of a downlink multicast or broadcast service (Multimedia Broadcast/Multicast Service (MBMS)) is transmitted through a downlink multicast channel (MCH). Uplink channels used to transmit data from the UE to the network include a Random Access Channel (RACH) used to transmit initial control messages and an uplink SCH used to transmit user traffic or control messages.
A logical channel is located above the transport channel and is mapped to the transport channel. The logical channel is mainly classified into a control logical channel and a traffic logical channel.
FIG. 4 illustrates conventional control channel transmission.
The physical channel includes a number of subframes in the time domain and a number of subcarriers in the frequency domain. One subframe includes a plurality of resource blocks, each of which includes a plurality of symbols and a plurality of subcarriers. In each subframe, specific subcarriers of specific symbols (for example, the first symbol) of the subframe can be used for a Physical Downlink Control Channel (PDCCH), i.e., an L1/L2 control channel, as shown in FIG. 4. One subframe corresponds to 0.5 ms and a Transmission Time Interval (TTI), which is a unit data transmission time, is 1 ms corresponding to two subframes.
A Multicast Control Channel (MCCH), which is a logical channel, or a Multicast Traffic Channel (MTCH) may be mapped to an MCH which is a transport channel for MBMS. The MCCH transmits an MBMS related RRC message and the MTCH transmits traffic of a specific MBMS service.
In the LTE system, MBMS data is transmitted through MBMS-dedicated Multimedia Broadcast multicast service Single Frequency Network (MBSFN) subframes.
One or more MTCHs mapped to one MCH are scheduled to MBSFN subframes at regular intervals. Scheduling information of one or more MTCHs mapped to one MCH is broadcast to UEs through MCH Scheduling Information (MSI) which is a MAC Control Element (MAC CE). The MSI is also referred to as “MBMS Dynamic Scheduling Information (DSI). Here, an MSI MAC CE for a specific MCH is updated at regular intervals through MBSFN subframes allocated to the specific MCH.
In the related art, MBSFN subframes scheduled through the MSI are always used only for transmission of the corresponding MTCH. That is, once MBSFN subframes are allocated for transmission of a specific MTCH, the allocated MBSFN subframes cannot be used for purposes other than MBMS during a corresponding MSI transmission period. Thus, in the case where various data rates are supported for a specific MBMS, some of the allocated MBSFN subframes may not be utilized during a specific time period, resulting in inefficient use of wireless resources.